MORPHOGENESIS IN STENTOR
21
the cell by excising the posterior half of the incipient posterior daughter
cell, the sausage-shaped nucleus then divides unequally, the level of
separation occurring wherever the constricting furrow happens to pinch
it in two.
A suggestive parallel is found in chromosomal diminution in Ascaris
development. The egg shows a gradient of certain materials in the cytoplasm and it is only in the upper cleavage products that loss of chromosomes occurs. Harrison (1935) cited this as the best case of the effect of
cytoplasm upon the nucleus. Mating type determination of the macronucleus in Type B Paramecium aurelia (Sonneborn, 1947) as well as
control of the nucleus by the cytoplasm in Stentor are new and striking
cases among the Protozoa.
D. Chimeras
Both nuclei and cytoplasms can be exchanged between stentors of
different species. Heterografts of whole cells remain firmly adherent
and nuclei persist in foreign cytoplasm so that there is ample basis for
testing interactions across the species line. In general I think it can be
said that in stentors there is about the same degree of incompatibility
as has been found in chimeras or various types of hybrids in Metazoa.
The epigenesis of new structures often occurs in some measure, showing
that an interaction between alien nuclei and cytoplasms is possible, but
the combinations are eventually overwhelmed by disharmonies which
terminate in death.
Combinations between S. coeruleus and S. polymorphus have been
the most extensively studied (Tartar, 1953; 1956c). Though the polymorphus nucleus may support initial oral regeneration in coeruleus
cytoplasm, the process does not go to completion and the anläge is
resorbed. Appreciable admixture of coeruleus cytoplasm causes polymorphus to extrude its symbiotic chlorellae, and conversely, a bit of
polymorphus leads to blanching or depigmentation of coeruleus. At first
it appeared that in cell grafts between these two species the larger
component became dominant and assimilated the other, but more
recently (Tartar, 1960a) it has been found that a relatively small bit of
nucleated polymorphus grafted to a large coeruleus often does maintain
its deleterious influence, resulting in the eventual death of the chimera
which becomes entirely colourless, devoid of both pigment and chlorellae,
and may even pass into a chaotic state very much like the 'cancerous'
stentors described previously.
Among many negative cases a few instances were found in which the
nucleus of the blue-green but otherwise quite different S. introversus
supported complete oral regeneration in coeruleus, but the chimera then
died after a few days. Whether the form of the cell elaborations is
B
A . M . 2
21
the cell by excising the posterior half of the incipient posterior daughter
cell, the sausage-shaped nucleus then divides unequally, the level of
separation occurring wherever the constricting furrow happens to pinch
it in two.
A suggestive parallel is found in chromosomal diminution in Ascaris
development. The egg shows a gradient of certain materials in the cytoplasm and it is only in the upper cleavage products that loss of chromosomes occurs. Harrison (1935) cited this as the best case of the effect of
cytoplasm upon the nucleus. Mating type determination of the macronucleus in Type B Paramecium aurelia (Sonneborn, 1947) as well as
control of the nucleus by the cytoplasm in Stentor are new and striking
cases among the Protozoa.
D. Chimeras
Both nuclei and cytoplasms can be exchanged between stentors of
different species. Heterografts of whole cells remain firmly adherent
and nuclei persist in foreign cytoplasm so that there is ample basis for
testing interactions across the species line. In general I think it can be
said that in stentors there is about the same degree of incompatibility
as has been found in chimeras or various types of hybrids in Metazoa.
The epigenesis of new structures often occurs in some measure, showing
that an interaction between alien nuclei and cytoplasms is possible, but
the combinations are eventually overwhelmed by disharmonies which
terminate in death.
Combinations between S. coeruleus and S. polymorphus have been
the most extensively studied (Tartar, 1953; 1956c). Though the polymorphus nucleus may support initial oral regeneration in coeruleus
cytoplasm, the process does not go to completion and the anläge is
resorbed. Appreciable admixture of coeruleus cytoplasm causes polymorphus to extrude its symbiotic chlorellae, and conversely, a bit of
polymorphus leads to blanching or depigmentation of coeruleus. At first
it appeared that in cell grafts between these two species the larger
component became dominant and assimilated the other, but more
recently (Tartar, 1960a) it has been found that a relatively small bit of
nucleated polymorphus grafted to a large coeruleus often does maintain
its deleterious influence, resulting in the eventual death of the chimera
which becomes entirely colourless, devoid of both pigment and chlorellae,
and may even pass into a chaotic state very much like the 'cancerous'
stentors described previously.
Among many negative cases a few instances were found in which the
nucleus of the blue-green but otherwise quite different S. introversus
supported complete oral regeneration in coeruleus, but the chimera then
died after a few days. Whether the form of the cell elaborations is
B
A . M . 2